Update E0297 to new error format

src/test/compile-fail/E0297.rs

@@ -11,5 +11,7 @@
 fn main() {
     let xs : Vec<Option<i32>> = vec!(Some(1), None);
 
-    for Some(x) in xs {} //~ ERROR E0297
+    for Some(x) in xs {}
+    //~^ ERROR E0297
+    //~| NOTE pattern `None` not covered
 }